Why on earth? Because the treat will deliver a vaccine against a disease that is wiping out prairie dogs–and their endangered predators.

For the endangered black-footed ferret–an adorable if vicious predator that lives in prairies–one of the biggest threats to survival is the bubonic plague, which is wiping out their prey: prairie dogs.

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To help, the U.S. Fish and Wildlife Service hopes to start using drones to spray candy-sized snacks, filled with plague vaccine, across prairie dog colonies. Without the prairie dogs, the ferrets can’t survive; the dogs are both a food source and a source of a burrow.

Ferrets likely migrated across the Bering Land Bridge thousands of years ago, and when they discovered millions of prairie dogs in North America, they evolved to depend on them.

“Prairie dogs were seemingly an infinite resource for food, and as a bonus, you killed the owner, you ate him, and then you got the house,” says Ryan Moehring, public affairs officer for the Fish and Wildlife Service. “In some respects, they’re like the worst possible neighbor. But they’re incredibly cute.”

Here’s a rare glimpse of the nocturnal ferret in the daytime, and its skirmish with a prairie dog:

The two animals coexisted for thousands of years. But as settlers moved west, systematically plowing up prairies and poisoning and shooting prairie dogs, the situation changed. At first, Western settlers didn’t even realize that ferrets existed, because they live underground and are nocturnal. By the modern era, experts thought they were extinct. But in 1979, by chance, a single remaining colony of ferrets was discovered.

“What ended up happening was that colony was infected by plague, and it started wiping them out,” says Moehring. “By the time we got in there and started capturing the last remaining ferrets, there were only a handful, 20 individuals, of which 18 survived.”

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The Wildlife Service bred the remaining ferrets in captivity and started releasing them into the wild. But certain non-native diseases, such as canine distemper and the plague, can easily kill them. The ferrets can be vaccinated before release, but the prairie dogs can’t. “You can’t catch them all and give them shots,” he says. “It doesn’t make any sense.”

Instead, officials have been trying to fight the disease through a cumbersome process of trying to find every prairie dog hole–inside prairie dog “towns” that are a mile wide and a mile long–and spraying insecticide in the holes in the hope of killing the fleas that carry the plague.

“You can imagine that’s very, very time consuming, cost prohibitive, and inefficient,” says Moehring. “So we thought, well, what if we looked at this another way–we innoculate the ferrets to vaccinate them against the plague, why can’t we vaccinate prairie dogs?”

Working with a group of partners like the World Wildlife Fund, the team carefully designed tiny pellets that look a little like M&Ms. “They’re basically a proprietary food blend that has peanut butter in it,” he says. “Apparently everybody and everything likes peanut butter.” In trials, prairie dogs ate 90% of the snacks. The pellets also have a little food-grade dye inside, so the prairie dogs’ whiskers (and poop) are marked when they eat the vaccine.

The researchers proposed two approaches: in one scenario, they’d deliver the vaccines by hand. But in another, they’d make use of drones to more easily spread the vaccine over large areas. An attachment would need to be designed to shoot the pellets from the top of the drone, and it could potentially cover an acre in less than a minute.

The location, the UL Bend National Wildlife Refuge in northeastern Montana, is an ideal test site. It’s remote and far from air traffic, so drones wouldn’t interfere with planes. If it works, the technique might eventually be used in some of the other 27 sites where ferrets have been reintroduced. But in each case, the drones would have to go through an approval process.

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Fish and Wildlife Service officials prepared a full environmental assessments for both hand delivery and drone delivery and are waiting for approval as the proposals go through a public comment period.

The vaccine might be the key to the ferrets’ survival.

“We’re committed to saving this critter,” he says. “We’ll explore any reasonable means to do that, even if that includes some unconventional ideas like shooting peanut butter pellets from a drone.”

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About the author

Adele Peters is a staff writer at Fast Company who focuses on solutions to some of the world's largest problems, from climate change to homelessness. Previously, she worked with GOOD, BioLite, and the Sustainable Products and Solutions program at UC Berkeley, and contributed to the second edition of the bestselling book "Worldchanging: A User's Guide for the 21st Century."